Gas turbines operate by combusting fuel in a combustion system or a plurality of combustors to create a high-energy combustion gas that passes through a turbine, thereby causing a turbine rotor shaft to rotate. The rotational energy of the rotor shaft may be converted to electrical energy via a generator coupled to the rotor shaft. Each combustor generally includes fuel nozzles that may provide premixing of the fuel and air upstream of the combustion zone, as a means to keep nitrogen oxide (NOx) emissions low.
Gaseous fuels, such as natural gas, often are employed as a combustible fluid in gas turbine engines used to generate electricity. In some instances, it may be desirable for the combustion system to be able to combust liquid fuels, such as distillate oil, with no changes to the combustion hardware. A configuration with both gas and liquid fuel capability is called a “dual fuel” combustion system. In a typical configuration, the liquid fuel injection is provided though cartridges that fit in the center of the gas premixing fuel nozzles.
To provide an operator of the gas turbine with the ability to switch between gas-only operation and dual-fuel operation, conventional fuel nozzles may be installed with blank or dummy cartridges that may be easily replaced with liquid fuel cartridges. These blank cartridges, which are used for gas-only operation, merely fill the space in the center of the fuel nozzle that may eventually be occupied by a liquid fuel cartridge. The blank cartridges are typically purged with air to cool the tips of the cartridges, which face the combustion zone, to keep the tips at an acceptable temperature.
A large portion of gas turbine operators rely primarily on the combustion of gaseous fuels and employ the gas only configuration of the combustion system. During operation the combustion system directs purge flow through or around a tip portion of the blank cartridge. While this purge flow is generally a small fraction of the total flow through the combustor, the purge flow does not participate in the fuel/air premixing prior to combustion and, thus, does not contribute to a reduction in NOx emissions. It is generally desirable and often required by regulations to keep gas turbine NOx emissions at the lowest achievable level.